You realize what you're suggesting entails carrying around something on the order of 20 or so weapons, right? Assuming you want to dual wield the weapons you are going to choose to exploit your opponent's lack of skill in that weapon. And assuming you have more than just one or two of the two weapons you spec in.

That's obviously impossible, nobody could carry all that around.

Even more of a problem is that your theory that using a weapon that the enemy can't parry is so uber powerful. It's not. Especially against people with dam redux.

Lastly, let's consider your options if you use non-spec weapons. An example is helpful. You bust out those two daggers to fight the shaman who does not know how to use daggers. You can't bash him. You probably can't trip him. What now? Kick? Feinting his two attacks per round?

People have specs for a reason. Warriors didn't need them so much long ago because other classes weren't so diverse in their skills and powers. But now those other classes, like warriors, have been expanded enormously. The specs are something which make warriors overpower, it makes them playable against the other classes which over time have also received, in the words of forum junkies, lovin'.